1. Field of the Invention
This invention relates to the use of a conductive polymer material to selectively control, on the basis of wavelength, the light transmission through a transparent or semi-transparent panel or film; and more particularly to the use of a conductive polymer material to provide a window shade with high transmittance in a visible light range and high reflectance and absorbance in a near and far infrared range. Such a device may be embodied as a flexible plastic sheet, or as an integral part of a mutiple-pane insulating window panel.
2. Description of the Prior Art
Thermal-pane windows in which spaced multiple (two or more) panes provide a thermal barrier restricting heat conduction between the outside and the inside of a building are conventionally used to reduce heating and cooling costs. To further reduce cooling costs, window shades or blinds are used to block out intense, direct rays of sunlight, since conventional windows, insulating or otherwise, have little effect on radiative heating. In using conventional shades to eliminate solar glare, the view to the outside is blocked, creating a visually unattractive result. Products utilizing low emissivity glazing attempt to overcome the shortcomings of ordinary glass windows by covering glass or plastic film with a metal or metal oxide coating (e.g., HEAT MIRROR.TM. manufactured by Southwall Technologies of Palo Alto, CA or SCOTCHTINT.TM. manufactured by 3M Company of Minniapolis, MN.). This type of glazing offers transparency to visible light while partially blocking (reflecting) the infrared. There is, however, a need for increasing the degree of reflection and absorption of solar infrared radiation while maintaining substantially the same degree of transparency to visible light. There is also a need for reducing the cost of the present coated films.
Thus, there exists a need for a low cost, easy-to-fabricate window glazing which includes a coating that permits a high degree of coherent light transmission in the visible region of the electromagnetic spectrum and is highly reflective and absorbing in the near infrared (NIR) region and optionally in the far infrared (FIR) region. Such a window glazing can be used to limit radiative heating from the sun's rays (near-IR blocking) without blocking or obscuring the view from the outside. The characteristic of being reflective in the far IR limits passage of thermal (black body) radiation through the window, keeping the interior of a building or vehicle cool in summer and warm in winter.
Conjugated backbone polymers, e.g., polyacetylene, polyphenylene, polyacenes, polythiophene, poly(phenylene vinylene), poly(thienylene vinylene), poly(furylene vinylene), polyazulene, poly(phenylene sulfide), poly(phenylene oxide), polythianthrene, poly(isothianaphthene), poly(phenylquinoline), polyaniline, and polypyrrole, and the like have been suggested for use in a variety of electronic applications based upon their characteristic of becoming conductive when oxidized or reduced either chemically or electrochemically. Electrodes composed of such polymers can, according to the method of MacDiarmid et al. in U.S. Pat. No. 4,321,114, be reversibly electrochemically reduced to an n-type conductive state (the polymer being inserted by cations) or reversibly oxidized to a p-type conductive state (the polymer being inserted by anions).
The electrochemical oxidation or reduction process is generally recognized to be accompanied by sharp changes in the color of the polymer as well as its optical absorption coefficient (its ability to transmit light). An adjustable tint window based on the electrochemical switching of conductive polymers has been disclosed in a Wolf et al., U.S. Pat. application Ser. No. 211,537, filed June 27, 1988.
The adjustable tint window of Wolf et al is complex, requiring electrical circuitry, an electolyte and electrodes, which increase its cost.